Tandy 1400LT Service Manual page 100

Signal Name 1 / 0 Description
ECLK
*BRST
AO-A 19
DO-D7
ALE
IOREDY
IRQ 2,3,5
*EIR
*EIW
*EMR
*EMW
D R 1 & 3
*DACKO,l
&3
BEN
*TC
*ENABLE
+
5 v
G N D
0
0
0
0
0
0
I
0
0
0
0
I
0
0
0
0
-+
+
Clock: This is the system clock. It has 2 speed modes. (4.77MHz, 7.16MHz). The clock has a
50% duty cycle
RESET: This is a the system reset. This signal is synchronized to the falling edge of clock and
is active LOW
Address Bits 0-19: These lines are generated by either the CPU (V20) or the DMA controller
(82C37). They are active HIGH.
Data Bits 0-7: These lines are active HIGH.
Address Latch Enable: This is provided by the Bus Controller (pPD71088). The CPU
addresses are latched with the falling edge of ALE.
I/O Channel Ready: This line is pulled low by a memory or 1 / 0 device to lengthen 1/0 or
memory cycle.
Interrupt Requests 2,3,5: These lines are used to signal the processor that an I/O device
requires attention.
I/O Read Strobe: This signal is active LOW.
1/0 Write Strobe: This signal is active LOW.
Memory Read Strobe: This signal is active LOW.
Memory Write Strobe: This signal is active LOW.
DMA Requests 1 and 3: These lines are asynchronous channel requests used by peripheral
devices to gain DMA service. A request is generated by bringing D R l and, 3 lines must be
held high until the corresponding DACK line goes active.
DMA Acknowledge 0, 1 & 3: These lines are used to acknowledge DMA requests and refresh
system DRAM (DACKO). They are active LOW.
Address Enable: This line is used to degate the CPU and other devices from the 1/0 channel
to allow DMA transfers to take place. This signal is active HIGH. When this line is
HIGH, the DMA Controller (82C37) has control of the lines (address bus, data bus read
and write strobe: memory and I/O)
Terminal Count: This line provides a pulse when the terminal count for DMA channel is
reached. This signal is active LOW.
ENABLE: This line maintains a High level when internal devices are selected (ROM. RAM,
VRAM, and I/O)
-t 5V
+
1 %, -5% Max 200m Amps available on the bus.
Power Return for +5V
4-63